Plain bearings

ABSTRACT

This invention consists of a plain bearing in which the bearing surface consists of or includes poly-phenylene sulphide to give good bearing properties and also because such linings can be bonded to backings of steel or aluminium or aluminium alloys with a bond that withstands hard operating conditions, for example changes of temperature and changes of shape and stress. The linear polymer can be cross-linked to a desired extent by appropriate treatment.

This is a Continuation of Application Ser. No. 736,337, filed Oct. 28,1976, now abandoned, which is a Division of Ser. No. 620,754, filed Oct.8, 1975, now U.S. Pat. No. 4,015,949, which is in turn a Continuation ofSer. No. 402,334, filed Oct. 1, 1973, now abandoned.

This invention relates to plain bearings and methods of making them, andmore particularly to a plain bearing having a bearing lining consistingof polyphenylene sulphide. Poly-phenylene sulphide is a crystallinematerial prepared by the reaction of p-dichlorobenzene with sodiumsulphide in a polar solvent. The linear polymer so formed, initially, ascharacterized by only fair mechanical strength. Upon heat curing in air,however, it is cross-linked into a tough, ductile, and extemelyinsoluble material. In this specification the term polyphenylenesulphide includes polymers of varying degrees of cross-linking which canbe produced depending upon the, heat treatment used.

Preferably, the bearing has a metal backing which is composed of, forexample steel, aluminium, or an aluminium alloy. When the backing ismade of steel, the upper surface of the backing can be aluminized, orcan have bonded to it, possibly by roll-bonding, a strip of aluminiumfoil, since polyphenylene sulphide will adhere more readily to aluminiumor to an aluminium alloy. Manganese dioxide, or lead oxide, may be mixedwith the poly-phenylene sulphide to assist cross-linking and to effectoxidation of the backing surface to improve the bond between thepolyphenylene sulphide and the backing. Alternatively, or in additionthereto, titanium dioxide can be added to improve the adhesion of thepoly-phenylene sulphide to the backing.

The bearing may be for wet or dry use, that is to say, it may bearranged to operate with oil, grease, or other appropriate lubricant.When made for wet uses, lubricant pockets can be provided in the lining,possibly by indenting into the backing, and can be charged withsufficient lubricant to last the life of the bearing. Alternatively, thebearings may be used as so called dry bearings by includingpolytetrafluoroethylene with the poly-phenylene sulphide layer.

The poly-phenylene sulphide may include fillers for improving themechanical properties or the lubricating properties, for example,copper, or bronze powders, asbestos, molybdenum disulphide, lead powder,lead oxide powder, cadmium, nickel, cobalt, or boron nitride.

From another aspect the invention may be considered to reside in a plainbearing having an overlay.

A soft overlay is often applied to the bearing surface of plainbearings, such as when the bearings are intended for use in a crankshaftbearing of an internal combustion engine. Such an overlay may be appliedby electrodeposition of such alloys as lead/tin, lead/tin/copper orlead/indium. The function of the overlay is to improve the seizureresistance of the bearing, to embed dirt particles carried by thelubricating oil, and, in some cases, to provide protection for thebearing against corrosion by the oil. The function of the tin or indiumcontent in the overlay is to make the overlay itself resistant tocorrosion. The thickness of the overlay must also be closely controlled,usually within the limits of ±0.01 mm.

Overlay plating is used on a range of bearing materials of the kindwhere there is a steel back, an intermediate alloy layer of copper/lead,lead/bronze, aluminium/tin or aluminium/silicon, and an overlay overthis intermediate layer. Preparation of the intermediate alloy surface,prior to electrodeposition of the overlay, is a multistage processinvolving one or more chemical etching stages, and, in the case, of thealuminium alloys, the electrodeposition of a tin interlayer of nickel orcopper. The electrodeposition of overlays is thus a complex processrequiring close control; it is for this reason a costly process whichaccounts for a significant proportion of the control cost of thebearing.

The common electrodeposited overlays have a further disadvantage in thatduring operating at high temperatures as might be experienced when thebearing is used in internal combustion engines, the loss of tin orindium by diffusion into the intermediate alloy or into the nickel orcopper interlayer can take place. When the overlay becomes denuded oftin or indium the overlay becomes subject to corrosion by the engineoil. Corrosion can result in severe cases in the partial or completedisappearance of the overlay.

A layer of poly-phenylene sulphide may be applied over such a plainbearing as a protective overlay.

The invention relates to all kinds of plain bearings whether thrust orjournal bearings, including plain shell bearings, for such applicationsas engine shaft bearings, and also plain bearings consisting of flatrelatively slidable metal surfaces of which many examples occur in theworld of engineering. A journal bearing shell can be made by coating aflat strip with poly-phenylene sulphide and then forming the strip intoa part cylindrical shell.

The poly-phenylene sulphide may be applied to the backing possibly inpowder form, or possibly in the form of a thin sheet, or possibly byspraying, for example, electro-static spraying, spraying in solution,plasma or flame spraying or even by application from a fluidised bed.

The bonding to the backing can be simply effected by heating the liningmaterial and backing or overlay sufficiently to melt the liningmaterial, and continuing heat treatment until a good bond is achieved.For example, in bonding polyphenylene sulphide to an aluminium alloy,such as, a magnesium/aluminium, silicon/aluminium or tin/aluminiumalloy, the resin is heated to at least 370° C. in air for at least 10minutes. Alternatively bonding can be effected by a rolling process andindeed a rolling process can also be used to form indentations in thelining to define the lubricant pockets discussed above.

Heat treatment of the poly-phenylene sulphide can cause an increaseddegree of cross-linking of the polymer which can improve its mechanicalproperties.

In general, the poly-phenylene sulphide layer will not soften in use attemperatures below 270° C. which is adequate as a bearing surfaceoperating temperature for very many applications.

The bearing can be bonded, formed and cured in operations which producequite severe deformations in the plastic/metal laminate without failureof the bond and without loss of manufacturing tolerance, and that makesthe poly-phenylene sulphide particularly suitable for the type ofbearing which requires such formation.

Another method of keying the poly-phenylene sulphide to the backing isby causing the layer of metal powder to adhere to the backing, and thenimpregnating it with the poly-phenylene sulphide, for example, byrolling. As poly-phenylene sulphide is dimensionally stable it ispossible to form bearings of the final size in that manner but it ispossible to machine the bearing to the final size for example by boring.

Also where a particular thickness of poly-phenylene sulphide is requiredit may be built up in one or more layers.

The invention may be carried into practice in various ways and someexamples will now be described.

EXAMPLE I

A 1 mm thick strip of an alloy of 4.0 to 4.9% magnesium by weight, 0.5to 1.0% manganese, with the balance aluminium, is brushed under arotating wire brush and has applied to it poly-phenylene sulphide powderwith a particle size in the range 90 to 350 microns, the powder havingbeen lightly cross-linked by heat treatment in air. The powder is spreadby a reciprocating blade to a thickness of 2 mm and is then melted byheating at 300° C. from the aluminium alloy side. Then the melted layeris transferred to an oven and cured for one hour at 375° C. achieving afinal layer thickness in the range 0.3 to 0.4 mm. Bearing brushes areformed from such a strip blank.

EXAMPLE II

A low carbon steel strip 1.5 mm thick is linished and has bonded to it abrushed commercially pure aluminium foil 0.1 mm thick and bonding iseffected by rolling with 43% reduction. The upper aluminium surface isbrushed and then the lining is applied to it by the method described inExample I. In either case the temperature at which the finished bearingbegins to distort can be raised by a long curing step, for examplecuring at 375° C. for 16 hours.

EXAMPLE III

This method is the same as in Example I except that after the polymerhas melted the strip is cooled rapidly and formed into a bush which isthen heated at 375° C. for one hour.

EXAMPLE IV

This method is the same as Example III except that instead of coolingthe strip rapidly the following heat treating cycle is followed: heatingfor one minute between 300° and 375° C., holding for five minutes at375° C., and heating for 15 minutes at 375° to 440° C.

EXAMPLE V

This is the same as Example I except that the strip is a 1 mm thickstrip of an alloy consisting of 0.8 to 1.5% manganese by weight with thebalance being aluminium. After curing the strip is passed under anindenting roll to give a pattern of 2 mm by 1 mm rectangular indents 0.4mm deep. The blank is formed into part-cylindrical portions with theindents extending axially and the indents are filled with grease priorto use.

EXAMPLE VI

This is the same as Example V up to identation, after which a blank isrolled in low molecular weight polyethylene wax and formed into a bush.

EXAMPLE VII

A drawn tube 30 mm inside diameter and 35 mm outside diameter and 50 mmlong of an alloy consisting of 3.1 to 3.9% magnesium by weight with thebalance being aluminium is degreased and heated to 520° C. It is thendipped into a fluidised bed of lightly cross-linked poly-phenylenesulphide powder which melts on the surface. Unmelted powder is removedby blowing or sucking and the coated tube transferred to an oven at 310°C. The temperature is raised to 375° C. for one hour and the tube ismachined to final size.

EXAMPLE VIII

A shell consisting of a 60% aluminium/40% tin alloy has its surfacebrushed and applied to a cleaned surface of a steel backing. The backingand lining are heated to 400° C. and then treated as in Example VII.

EXAMPLE IX

Poly-phenylene sulphide powder which is not cross-linked is mixed withDQ3 powder in a high speed mixer in equal proportions, and spread by areciprocating blade in a layer 1 mm thick on a brushed surface of a 1 mmthick strip of alloy consisting of 4.0 to 4.9% magnesium, 0.5 to 1.0%manganese, the balance being aluminium. The powder is melted at 300° C.by heating from the aluminium side and consolidation bonding is effectedwith a cooled roll after which the blank is cured for one hour at 375°C. cooled and formed into a bush.

EXAMPLE X

75 parts of poly-phenylene sulphide powder not cross-linked is meltedand combined with 25 parts of DQ3 powder and comminuted to a particlesize between 90 and 350 microns and it is then applied to a strip as inExample VII.

In the above two examples, DQ3 powder consists of:

    ______________________________________                                        PTFE                26.8% by weight:                                          Pb.sub.3 O.sub.4    65.0%                                                     PbO.sub.2            3.7%                                                     Tin/Bronze powder    4.5%                                                     ______________________________________                                    

EXAMPLE XI

This is the same as Example VIII but applied to an alloy consists of10.3% to 11% silicon, 0.9% to 11% copper, the balance being aluminium.

In the examples a temperature of 375° C. has been referred to. In factthe temperature and time of treatment can be varied in accordance withrequirements between about 316° C. for three hours and about 427° C. for10 minutes.

What we claim as our invention and desire to secure by Letters Patentis:
 1. In a plain bearing for use in an internal combustion engine,which is lubricated with a lubricant consisting of an oil, theimprovement which comprises a steel backing having adhered thereto asoft bearing layer of an alloy selected from the group consisting ofcopper/lead, lead/bronze, aluminum/tin and aluminum/silicon, and havingadherent on said bearing layer a protective overlay of polyphenylenesulfide.
 2. In a plain bearing for use in an internal combustion engine,which is lubricated with a lubricant consisting of an oil, theimprovement which comprises a steel backing having adhered thereto asoft non-porous bearing layer of an alloy selected from the groupconsisting of copper/lead, lead/bronze, aluminum/tin and aluminumsilicon, and having adherent on said bearing layer a protective overlayof polyphenylene sulfide.